Kenji Kitamura1, Masanori Fujii2, Takeshi Utsunomiya1, Miho Iwamoto1, Satoshi Ikemura1, Satoshi Hamai1, Goro Motomura1, Mitsugu Todo3, Yasuharu Nakashima1. 1. Department of Orthopaedic Surgery, Graduate School of Medical Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan. 2. Department of Orthopaedic Surgery, Graduate School of Medical Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan. Electronic address: m-fujii@ortho.med.kyushu-u.ac.jp. 3. Research Institute for Applied Mechanics, Kyushu University, 6-1 Kasuga-koen, Kasuga 816-8580, Japan.
Abstract
BACKGROUND: Physiologic pelvic tilt can change acetabular orientation and coverage in patients with hip dysplasia. In this study, we aimed to clarify the impact of change in sagittal pelvic tilt on joint stress distribution in dysplastic hips. METHODS: We developed patient-specific finite element models of 21 dysplastic hips and 21 normal hips. The joint contact area, contact pressure, and equivalent stress of the acetabular cartilage were assessed at three pelvic tilt positions relative to the functional pelvic plane: 10° anterior tilt, no tilt, and 10° posterior tilt. FINDINGS: The mean contact area was 0.6-0.7 times smaller, the mean maximum contact pressure was 1.8-1.9 times higher, and the mean maximum equivalent stress was 1.3-2.8 times higher in dysplastic hips than in normal hips at all three pelvic positions. As the pelvis tilted from 10° anterior to 10° posterior, the mean contact area decreased, and the mean maximum contact pressure and median maximum equivalent stress increased. The latter two changes were more significant in dysplastic hips than in normal hips (total increment was 1.3 MPa vs. 0.4 MPa, P = 0.001, and 3.6 MPa vs. 0.4 MPa, P < 0.001, respectively). The mean equivalent stress increased in the anterosuperior acetabulum during posterior pelvic tilt in dysplastic and normal hips, while the change was not significant in the superior and posterosuperior acetabulum in both groups. INTERPRETATION: Sagittal pelvic tilt alters the loading environment and joint stress distribution of the hip joint and may impact the degeneration process in dysplastic hips.
BACKGROUND: Physiologic pelvic tilt can change acetabular orientation and coverage in patients with hip dysplasia. In this study, we aimed to clarify the impact of change in sagittal pelvic tilt on joint stress distribution in dysplastic hips. METHODS: We developed patient-specific finite element models of 21 dysplastic hips and 21 normal hips. The joint contact area, contact pressure, and equivalent stress of the acetabular cartilage were assessed at three pelvic tilt positions relative to the functional pelvic plane: 10° anterior tilt, no tilt, and 10° posterior tilt. FINDINGS: The mean contact area was 0.6-0.7 times smaller, the mean maximum contact pressure was 1.8-1.9 times higher, and the mean maximum equivalent stress was 1.3-2.8 times higher in dysplastic hips than in normal hips at all three pelvic positions. As the pelvis tilted from 10° anterior to 10° posterior, the mean contact area decreased, and the mean maximum contact pressure and median maximum equivalent stress increased. The latter two changes were more significant in dysplastic hips than in normal hips (total increment was 1.3 MPa vs. 0.4 MPa, P = 0.001, and 3.6 MPa vs. 0.4 MPa, P < 0.001, respectively). The mean equivalent stress increased in the anterosuperior acetabulum during posterior pelvic tilt in dysplastic and normal hips, while the change was not significant in the superior and posterosuperior acetabulum in both groups. INTERPRETATION: Sagittal pelvic tilt alters the loading environment and joint stress distribution of the hip joint and may impact the degeneration process in dysplastic hips.